The miniaturization of diamond parts, such as playback styli, has increased the need for reproducible, accurate machining of diamond parts to the micron and submicron levels. For example, U.S. Pat. No. 4,162,510 to Keizer discloses a diamond stylus for a high density information record playback system such as a video disc player, which is shaped so as to have a tip portion of only about 2 microns by 2 microns.
To form a stylus of the type disclosed by Keizer two facets are initially formed near the tip of a crystallographically oriented diamond bar to form a tip or prow on the diamond bar. The facets have heretofore been machined by a method which includes the use of a lapping apparatus such as that described in U.S. Pat. No. 4,321,772 to Ziegel. Such a lapping apparatus typically includes a high speed motor attached by a drive shaft to a drive plate on which a lapping disc is mounted. Typically, the lapping disc is made of a porous tool-steel disc which in use is coated with an abrasive slurry. The porous tool-steel disc serves as a rigid support to hold the abrasive slurry in place during lapping of a diamond article. A typical abrasive slurry comprises 0.1 micrometer diamond particles in oil. A diamond bar held in direct contact with the diamond-abrasive coated work surface of the rotating lapping disc can be lapped to various desired shapes and/or sizes. This prior art process takes a considerable amount of time, however, due to the extreme hardness of diamond.
It would be desirable to have an improved lapping method which could increase the rate of lapping. Also, since diamond exhibits directional variations in hardness due to the crystallographic structure a lapping method which is less sensitive to this directional hardness and which would provide a net decrease in machining time per facet would also be highly desirable.